<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
    <title>WebGPU Points w/size</title>
    <style>
      @import url(resources/webgpu-lesson.css);
html, body {
  margin: 0;       /* remove the default margin          */
  height: 100%;    /* make the html,body fill the page   */
}
canvas {
  display: block;  /* make the canvas act like a block   */
  width: 100%;     /* make the canvas fill its container */
  height: 100%;
}
    </style>
  </head>
  <body>
    <canvas></canvas>
  </body>
  <script type="module">
async function main() {
  const adapter = await navigator.gpu?.requestAdapter();
  const device = await adapter?.requestDevice();
  if (!device) {
    fail('need a browser that supports WebGPU');
    return;
  }

  // Get a WebGPU context from the canvas and configure it
  const canvas = document.querySelector('canvas');
  const context = canvas.getContext('webgpu');
  const presentationFormat = navigator.gpu.getPreferredCanvasFormat();
  context.configure({
    device,
    format: presentationFormat,
  });

  const module = device.createShaderModule({
    code: /* wgsl */ `
      struct Vertex {
        @location(0) position: vec2f,
        @location(1) size: f32,
      };

      struct Uniforms {
        resolution: vec2f,
      };

      struct VSOutput {
        @builtin(position) position: vec4f,
      };

      @group(0) @binding(0) var<uniform> uni: Uniforms;

      @vertex fn vs(
          vert: Vertex,
          @builtin(vertex_index) vNdx: u32,
      ) -> VSOutput {
        let points = array(
          vec2f(-1, -1),
          vec2f( 1, -1),
          vec2f(-1,  1),
          vec2f(-1,  1),
          vec2f( 1, -1),
          vec2f( 1,  1),
        );
        var vsOut: VSOutput;
        let pos = points[vNdx];
        vsOut.position = vec4f(vert.position + pos * vert.size / uni.resolution, 0, 1);
        return vsOut;
      }

      @fragment fn fs(vsOut: VSOutput) -> @location(0) vec4f {
        return vec4f(1, 1, 0, 1); // yellow
      }
    `,
  });

  const pipeline = device.createRenderPipeline({
    label: 'sizeable points',
    layout: 'auto',
    vertex: {
      module,
      buffers: [
        {
          arrayStride: (2 + 1) * 4, // 3 floats, 4 bytes each
          stepMode: 'instance',
          attributes: [
            {shaderLocation: 0, offset: 0, format: 'float32x2'},  // position
            {shaderLocation: 1, offset: 8, format: 'float32'},  // size
          ],
        },
      ],
    },
    fragment: {
      module,
      targets: [{ format: presentationFormat }],
    },
  });

  const rand = (min, max) => min + Math.random() * (max - min);

  const kNumPoints = 100;
  const vertexData = new Float32Array(kNumPoints * 3);
  for (let i = 0; i < kNumPoints; ++i) {
    const offset = i * 3;
    vertexData[offset + 0] = rand(-1, 1);
    vertexData[offset + 1] = rand(-1, 1);
    vertexData[offset + 2] = rand(1, 32);
  }

  const vertexBuffer = device.createBuffer({
    label: 'vertex buffer vertices',
    size: vertexData.byteLength,
    usage: GPUBufferUsage.VERTEX | GPUBufferUsage.COPY_DST,
  });
  device.queue.writeBuffer(vertexBuffer, 0, vertexData);

  const uniformValues = new Float32Array(2);
  const uniformBuffer = device.createBuffer({
    size: uniformValues.byteLength,
    usage: GPUBufferUsage.UNIFORM | GPUBufferUsage.COPY_DST,
  });
  const kResolutionOffset = 0;
  const resolutionValue = uniformValues.subarray(
      kResolutionOffset, kResolutionOffset + 2);

  const bindGroup = device.createBindGroup({
    layout: pipeline.getBindGroupLayout(0),
    entries: [
      { binding: 0, resource: { buffer: uniformBuffer }},
    ],
  });

  const renderPassDescriptor = {
    label: 'our basic canvas renderPass',
    colorAttachments: [
      {
        // view: <- to be filled out when we render
        clearValue: [0.3, 0.3, 0.3, 1],
        loadOp: 'clear',
        storeOp: 'store',
      },
    ],
  };

  function render() {
    // Get the current texture from the canvas context and
    // set it as the texture to render to.
    const canvasTexture = context.getCurrentTexture();
    renderPassDescriptor.colorAttachments[0].view =
        canvasTexture.createView();

    // Update the resolution in the uniform buffer
    resolutionValue.set([canvasTexture.width, canvasTexture.height]);
    device.queue.writeBuffer(uniformBuffer, 0, uniformValues);

    const encoder = device.createCommandEncoder();
    const pass = encoder.beginRenderPass(renderPassDescriptor);
    pass.setPipeline(pipeline);
    pass.setVertexBuffer(0, vertexBuffer);
    pass.setBindGroup(0, bindGroup);
    pass.draw(6, kNumPoints);
    pass.end();

    const commandBuffer = encoder.finish();
    device.queue.submit([commandBuffer]);
  }

  const observer = new ResizeObserver(entries => {
    for (const entry of entries) {
      const canvas = entry.target;
      const width = entry.contentBoxSize[0].inlineSize;
      const height = entry.contentBoxSize[0].blockSize;
      canvas.width = Math.max(1, Math.min(width, device.limits.maxTextureDimension2D));
      canvas.height = Math.max(1, Math.min(height, device.limits.maxTextureDimension2D));
      // re-render
      render();
    }
  });
  observer.observe(canvas);
}

function fail(msg) {
  alert(msg);
}

main();
  </script>
</html>
